Butanol is an important industrial chemical, useful as a fuel additive, as a feedstock chemical in the plastics industry, and as a food grade extractant in the food and flavor industry. Each year 10 to 12 billion pounds of butanol are produced by petrochemical means and the need for this commodity chemical will likely increase in the future.
Methods for the chemical synthesis of the butanol isomer isobutanol are known, such as oxo synthesis, catalytic hydrogenation of carbon monoxide (Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 2003, Wiley-VCH Verlag GmbH and Co., Weinheim, Germany, Vol. 5, pp. 716-719) and Guerbet condensation of methanol with n-propanol (Carlini et al., J. Molec. Catal. A. Chem. 220:215-220, 2004). These processes use starting materials derived from petrochemicals. The production of isobutanol from plant-derived raw materials could minimize the use of fossil fuels and would represent an advance in the art.
U.S. Pat. No. 7,851,188 describes enzymatic pathways for the production of isobutanol in recombinant microorganisms. The penultimate step in one metabolic pathway described therein for the production of isobutanol is the conversion of α-ketoisovalerate to isobutyraldehyde. There remains a need in the art to identify additional enzymes that are suitable for use in isobutanol biosynthetic pathways.